Several multilamp arrangements employing various types of sequencing circuits have been described in the prior art, particularly in the past few years. A currently marketed photoflash unit, referred to as a flip flash, employs high-voltage type lamps adapted to be ignited sequentially by successively applied high-voltage firing pulses from a source such as a camera-shutter-actuated piezoelectric element. One type of flip flash unit comprises an elongated planar array of eight high-voltage type flashlamps mounted on a printed circuit board with an array of respectively associated reflectors disposed therebetween. The lamps are arranged in two groups of four disposed on the upper and lower halves respectively of the rectangular shaped circuit board. A set of terminal contacts at the lower end of the unit is provided for activation of the upper group of lamps, while a set of terminal contacts at the top of the unit is operatively associated with the lower group of four lamps. The application of successive high-voltage pulses (e.g., 500 to 4,000 volts from, say, a piezoelectric source controlled by the shutter of a camera in which the array is inserted) to the terminal contacts at the lower end of the unit causes the four lamps at the upper half of the array to be sequentially ignited. The array may then be turned end for end and again inserted into the camera in order to flash the remaining four lamps.
The circuit board used in the aforedescribed flip flash unit comprises a sheet of plastic having a pattern of conductive circuit traces, including the terminal contacts, on one side. The flashlamp leads are electrically connected to these circuit traces (e.g., by means of metal eyelets). The circuitry on the board includes six printed, normally open, connect switches that chemically change from a high to lower resistance, so as to become electrically conducting after exposure to the radiant energy from an ignited flashlamp operatively associated therewith. The purpose of these switches is to provide lamp sequencing and one-at-a-time flashing. The four lamps of each group are arranged in parallel with three of the four lamps being connected in series with their respective thermal connect switches. Initially, only the first of the group of four lamps is connected directly to the voltage pulse source. When this first group flashes, it causes its associated thermal connect switch (which is series connected with the next or second lamp) to become permanently conductive. Because of this action, the second lamp of the group of four is connected to the pulse source. This sequence of events is repeated until all four lamps have been flashed.
One problem experienced in circuits of the above variety is that if one lamp should short circuit internally upon flashing, the successive parallel lamps in the group of four will not flash. Accordingly, the remaining, unfired lamps are shorted. It has been found that this problem can be eliminated by the use of a radiant-energy-activated switch that is normally conducting and which becomes nonconducting subsequent to exposure to the actinic output of the flashlamp associated therewith. This disconnect switch is used in series with each of the lamps, except the last lamp, in a sequentially flashing parallel group of high voltage flashlamps. It may be used, if desired, in addition to the printed connect switches, which are normally open and which close upon actinic exposure. Hence, the modes of action of these two types of switches are opposite from one another--the disconnect switch interrupts the igniting circuit of the lamp in series with it upon firing of that lamp, while the thermal connect switch establishes the igniting circuit for the next lamp upon being activated.
A more recent version of the aforedescribed multilamp unit comprises a total of ten lamps arranged horizontally in two parallel columns, the lamps of one column being staggered relative to the lamps of the other column with the bases interdigitated and facing the adjacent column. A multiple reflector system for the lamps comprises a pair of adjacent strip-like reflector panels each having a column of side-by-side reflector cavities aligned with an associated column of lamps, the cavities of one panel being staggered with respect to the cavities of the other panel. Each panel is foreshortened with respect to the lamps associated therewith but covers the lead-in wires and substantial portions of the bases of lamps associated with the adjacent reflector panel. In this manner, the lead-in wires and base portions of lamps associated with one panel underlie the adjacent panel to be hidden thereby. This ten lamp unit also includes a circuit board and associated lamp-firing circuitry. Additionally, this latter unit may include both types of the aforedescribed switch members.
Examples of the above, eight lamp photoflash units are shown and described in U.S. Pat. Nos. 3,894,226 (Hanson), 4,047,015 (Blount), and 4,053,757 (Blount). A somewhat modified version of this product is described in U.S. Pat. No. 4,133,023 (Hanson) wherein horizontally oriented lamps are utilized. An example of a more recent ten lamp embodiment is shown and described in U.S. Pat. No. 4,164,007 (E. G. Audesse et al). Radiant energy activated switches which become conductive or non-conductive in response to receipt of the lamp's energy are shown and described in U.S. Pat. No. 4,130,857 (Brower).
It has been found that arcing can occur in the above units between the reflector and circuitry (including the switches forming a part thereof) which results in the conductive reflector serving as a ground to thus prevent firing pulses from reaching subsequent, unfired lamps. Arcing occurs primarily through openings located in the reflector, these openings provided for passage of radiant energy from the fired lamp to the respective switch member(s). The reflector, typically of a plastic material having a conductive, reflecting coating (e.g., aluminum) thereon, is located adjacent to (and in the case of the ten lamp versions, in contact with) the circuit board and its circuitry. To prevent such arcing, some units have utilized a totally nonconductive reflector (see U.S. Pat. No. 4,133,023 above) while others have taught using a layer of insulative material between the reflector and circuit board (see U.S. Pat. No. 3,894,226 above). Nonconductive reflectors have not proven acceptable because the reflecting materials (e.g., white enamel) used thereon lack the reflecting capability desired for photoflash products such as described above. Use of a layer of insulative material is also considered disadvantageous in view of the added costs thereof.
It is believed therefore that a photoflash unit which utilizes a reflector which in turn overcomes the aforementioned disadvantages of known reflectors would constitute an advancement in the art.